Here's a time-lapse video of the construction of Aida Cruises' new flagship, AIDAPrima, in Japan. The ship entered service in April this year. Watch in full-screen mode, and set the resolution to 2160p/4K (using the gearwheel icon at the foot of the video), for best results.
Looking at how they lower the engines and other major components into position, it's clear they don't expect to remove them during the life of the ship. They'd have to dismantle the vessel around them to get them out!